This invention relates to a bituminous roofing composition which comprises a block copolymer and a bituminous material. More particularly, this invention relates to a torchable roll roofing composition comprising the aforementioned ingredients and a third ingredient which assists in enhancing the composition's resistance to heat at roof top temperatures while at the same time enhancing flow at torching temperatures.
Asphalt is a common material utilized for the preparation of roofing members and coatings which may be applied as mopping grade asphalts, cutbacks in solvents, single ply membranes, shingles, roll roofing membranes, etc. While the material is suitable in many respects, it inherently is deficient in some physical properties which it would be highly desirable to improve. Efforts have been made in this direction by addition of certain conjugated diene rubbers, neoprene, resins, fillers and other materials for the modification of one or more of the physical properties of the asphalt binder. Each of these added materials modifies the asphalt in one respect or another but certain deficiencies can be noted in all compounds proposed. For example, some of them have excellent weather resistance, sealing and bonding properties but are often deficient with respect to warm tack, modulus, hardness and other physical properties.
Since the late 1960s, styrene-butadiene rubber and styrene-rubber block copolymers such as styrene-butadiene-styrene and styrene-isoprene-styrene block copolymers have been used to dramatically improve the thermal and mechanical properties of asphalts. Practical application of the rubber addition approach requires that the blended product retain improved properties and homogeneity during transportation, storage and processing. Long term performance of elastomer-modified asphalts also depends on the ability of the blend to maintain thermal and chemical stability.
To be suitable for synthetic roofing materials, the asphalt-block copolymer mixtures should meet the following requirements:
(a) sufficient resistance to flow at high temperatures, PA1 (b) sufficient flexibility at low temperatures, PA1 (c) workability according the convention methods used in the roofing technique, PA1 (d) adequate hot storage stability, PA1 (e) adequate hardness to prevent deformation during walking on the roof, and PA1 (f) if it is to be used as an adhesive, sufficient adhesion. PA1 1. Modem Size-Exclusion Liquid Chromatography, M. W. Yau, J. J. Kirkland, D. D. Bly, John Wiley and Sons, New York, N.Y., 1979. PA1 2. Light Scattering From Polymer Solutions, M. B. Huglin, ed., Academic Press, New York, N.Y., 1972. PA1 3. W. K. Kai and A. J. Havlik, Applied Optics, 12, 541 (1973). PA1 4. M. L. McConnell, American Laboratory, 63, May, 1978.
For roll roofing applications, it is preferred that the softening point (the temperature at which the material will tend to flow) be above about 250.degree. F., the cold bend temperature (the temperature at which the material will crack during application and service), which is not as critical a parameter as the others in this application, should be below about -5.degree. C., and that the asphalt and block copolymer components should be able to be mixed and processed at a temperature no higher than about 200.degree. C. to keep the asphalt heating costs down and to prevent softening of the polyester reinforcement commonly used in these membranes.
For roll roofing membranes, the bituminous composition is used to saturate and/or coat a reinforcing mat. The bitumen is there to make the membrane waterproof. The mat is used to aid in mechanical properties (gives the membrane strength, etc.). Polymer is added to the asphalt to improve the weatherability and mechanical properties of the asphalt.
Resistance to degradation under the application of heat at roof top temperatures is an important consideration in materials for roll roofing membranes. Roll roofing membranes are used, for example, to protect the surface of a roof. The membrane is rolled up and when applied, is merely unrolled in place on the roof. One application method to secure the membrane to the roof is torching, i.e. heating with a flame at a high temperature, perhaps close to 2000.degree. C. High performance roll roofing membranes which comprise a reinforcing mat coated with block copolymer modified asphalt must use a bituminous composition which flows sufficiently at these temperatures to ensure good application to the roof.
One method which has been used to increase the resistance of such compositions to heat at roof top temperatures and enhance flow at torching temperatures is to add an amount of atactic polypropylene to the bitumen/polymer blend. Membranes using such compositions are relatively easy to apply by torching because the atactic polypropylene has a sharp transition at its melting point and becomes a low viscosity material immediately. Thus, it is much easier to determine the point at which the torching should be discontinued than it is for materials like the block copolymers of the present invention which do not possess a sharp melting point.
Atactic polypropylene blends have the above advantages and are relatively low cost because they are easy to apply with relatively inexpensive equipment. However, they have the disadvantage that they are not elastic. This gives membranes made with such compositions a shorter life span because cracks form much more easily and are damaging to the surface because of the inelasticity of the composition.
Thus, it can be seen that it would be highly advantageous to be able to produce a bitumen/polymer blend for roll roofing which can be applied using relatively inexpensive equipment (flow characteristics) but which is also elastic. The present invention provides such a composition.